It seems strange Skype Broadcast has an upper limit of 10.000 participants and what will happen when you go over it? With LiveMeeting there is a limit of 1250 and number 1251 will receive an error message when trying to login. Will that also happen to number 10.001 when trying to login to a Skype Broadcast?
It's not a hard limit like in some other meeting scenarios. It's simply a limit of what we test and support. In talking with the team, I've learned the support boundary is mainly to preserve a good experience for all the little things that support the broadcast (e.g. Q&A, Yammer, etc.).
I heard this before about the limit of what you test. But in a company as big as Microsoft, testing with a larger audience should not be an issue? And Azure Media Services should be capable of handling much more participants.
But maybe the crucial factors are indeed Q&A, Yammer and the other stuff.